Apparatus for continuous reactive metal deposition in vacuum and its application

Abstract: Improvement in dielectric film deposition technique on plastic substrates generally destined to goods and alimentary products packaging, to optical coatings, etc. The invention places in the deposition equipments area with metal reaction, to utilise in continuous vacuum equipments. In comparison with the traditional techniques, plastic substrate (2) is exposed to metal source (6) by a multipass system, such to be exposed many times, for some instants, under said source obtaining in this way, a much more long time for react with the reactive gaseous surrounding, possibly activated. The equipment is essentially constituted by a roll-to-roll device having a multi-return returns (1) configuration situated in a zone (Z1) with different pressure in respect to the deposition zone (Z2), so to permit the reaction with process gas. This improved technique allows a notable saving in costs and treated film production.

Description: The invention concerns an apparatus to be used for reactive metal deposition in continuous vacuum equipments and a respective process. This invention overcomes the incoveniences found in preceding solutions as the substrate to be treated moves in a roll system, devised in a way to allow the metal to deposit from a reaction of reactive gas, possibly ionised and/or excited. In the last times the request for dielectric deposition films, especially on plastic flexible substrates increased. A typical example is the coating by dielectric film of plastic sheets (for example PE, PET, OPP) to realise barrier for oxygen and water vapour, transparent, for products destined to alimentary packaging; products sensible to oxygen and water vapour. However, dielectric films depositions, generally oxides, present remarkable difficulties in the process, when physical vapour deposition techniques (PVD: crucible evaporation, electron gun evaporation, sputtering, etc.); or chemical vapour deposition phase (CVD) is used. These problems are often connected to the difficulties caused by high speed deposition of said materials. A well known method to overcome problems of dielectric direct deposition is to vaporise metals in gaseous reactive environment, thereby obtaining, for instance, oxides or nitrides from these metals. This kind of process, well known in the thin films field, involves however, a restriction in the maximum speed of metal deposition, as the metal needs the time to completely react with the gaseous environment, optionally activated by ionisation and/or excitement. In the plastic film coatings, however, in continuous plants, constituted with traditional configurations such as described in documents US-A-2 665 228 and DE-A-3 046 564, it results to be quite impossible. In fact, the substrate sliding speed must be at least some metres per sec. and to obtain the desired thickness of some tens mm (hundreds Å) of dielectric, the instantaneous metal deposition rate is too high to obtain a complete reaction, as the operation is made at a pressure below 0.133 Pa (10 -3 Torr). It is the principal object of the present invention that the substrate maintains a sliding high speed providing a complete reaction of the metal, as the period in which the substrate is submitted to the oxidation is largely amplified by means of a series of short metal depositions followed by a long running in a reactive ambient. It is possible moreover, by traditional methods, that the pressure, in the deposition zone, results notably lower than that one obtained in the reaction zone, favouring on one hand the reactive processes, which are proportional to the partial pressure of reactive gas, on the other hand in a way that the depositing material does not suffer excessive interactions with the gaseous residual ambient which reducing energy, causes deterioration in deposed film compactness and its barrier properties thereto. The invention here presented is essentially constituted by a vacuum chamber 1 properly pumped, a sliding system for the plastic film, a system of rolls 3, 3a with many returns which has the task to increase the interaction surface of some orders of magnitude, a metal vaporisation device 6, a reactive gas introducing device, which can be activated by a variety of methods (i.e. UV sources, DC or RF discharge, microwave, ECR, ionic or plasma guns), a physical screen 7 able to separate Z1 and Z2 zones wich are at different pressures. A release of the invention, currently preferred by the inventors, is provided. It is evident however that different dimensions and configurations can be imposed provided the equipment maintains its characteristics which make it original. One of its characteristic aspects is the increasing time in which the entire film is deposited in a reactive way on the substrate. This is due to the distance between the series of rolls 3 and 3a. The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which: Fig. 1 is a view of the equipment; Fig. 2 is one of the possible rolls system configuration. In Fig. 1: 1 vacuum chamber; 2 substrate carried through two series of rolls 3 and 3a; 3, 3a rolls; 4 portion of substrate surface exposed to the source; 5 substrate spool roll; 6 metal source; 7 physic screen between Z1 and Z2 zones; 8 return rolls In Fig. 2: 3b rolls series 3c rolls series behind and screened in respect of the source. One of the possible ways to realise coating by the equipment given above is described in the following: Loading the spool of plastic material through the rolls system 3, 3a, such to assume a configuration like an accordion. The film 2 passes repeatedly the source for a short period and then transits in the reactive zone Z2 and is cyclically coming back attaining the coating end. The transits number is obviously equal to the number of the rolls. It is the principal object of the present invention to effect dielectric film deposition with high substrate speed, with vaporising sources at very low temperature and consequent abatement of work times and costs.

Claims: Apparatus for reactive metal deposition upon a web of a plastic film, comprising: a chamber with means for forming a vacuum in said chamber, adapted for containing in use a reactive atmosphere; a plurality of spaced apart rollers in said chamber defining a path for said web through said chamber, said path including at least one loop; a supply roll for feeding said web to said path; a take-up roll for receiving said web from said path; at least one source of metal vapour juxtaposed with only a first portion of said path for depositing in use a coating of said metal on said web, said chamber being subdivided into two zones including a first zone containing said at least one source, said first portion of said path, and adapted to be operated in use at one pressure, and a second zone containing a second portion of said path and adapted to be operated in use at a higher pressure than said one pressure in said first zone such that said coating is in use reacting in said reactive atmosphere in said second portion of said path, and means for exiting said reactive atmosphere in said second zone to promote reaction of the deposited metal therewith; said rollers including a multiplicity of rollers in said first and second zones defining at least one loop of said web along said path, said path including at least one pass through said first zone whereby said web is juxtaposed with said at least one source and whereby in use said coated web passes through said reactive atmosphere in said second zone for reaction of the metal coating therewith; said rollers further including an upper array of rollers and a lower array of rollers, said web being looped between upper and lower rollers of said arrays, some of the rollers of one of said arrays being placed lower than other rollers of said one of said arrays and being larger than rollers of the other of said arrays such that the curvature of said web, as said web in use passes around the rollers of said one of said arrays, is minimized. Apparatus as defined in claim 1, characterized by the fact to comprise means for heating said rollers. Apparatus as defined in claim 1, characterized by the fact to comprise means for cooling said rollers. Apparatus as defined in claim 1, characterized by the fact that said rollers are located within the chamber. Apparatus as defined in claims 1 - 4, characterized by the fact that there are provided a plurality of sources of metal vapour in said first zone, and/or a plurality of loops of said web along said path through said first and second zones. Use of the apparatus of claims 1 - 5 in a process for reactive thin film deposition such as to provide a multiple step deposition/reactive atmosphere treatment cycle.

Inventors: MISIANO CARLO, SIMONETTI ENRICO, MISIANO, CARLO, SIMONETTI, ENRICO
Applicants: CETEV CENT TECNOLOG VUOTO, CE.TE.V. CENTRO TECNOLOGIE DEL VUOTO
Application year: 1994
Main classification: C23C14
IPC codes: C23C14